(Tribune News Service) — Researchers say they have found a new clue in the sinking of the Confederate submarine H.L. Hunley, the first combat submarine that sank the USS Housatonic off Charleston, S.C., in 1864. New clues show a broken pipe may have been to blame.

The Hunley vanished soon after it became the first submarine to sink a warship during a battle. The vessel was lost until 1995. Archeologists raised the ship in 2000 and have been working to solve the mystery of why the sub sank ever since, Smithsonian Magazine reports.

Conservators with Clemson University have been cleaning the Hunley of the “concretion — the rock-hard layer of sand, shell and sea life — that gradually encased the Hunley during the nearly 136 years she rested on the sea floor,” according to a news release from The Hunley Project.

The researchers found a broken intake pipe that may have allowed water to flood the submarine. They found a 1-inch gap where the pipe was supposed to connect to the wall of the submarine, according to the release.

Scientists on the project warned, “This new evidence is not conclusive.”

“Unfortunately, there are no easy answers when investigating what led to a complex 150-year-old sinking. Still, this is a very significant discovery that will help us tell the full story of the Hunley’s important chapter in naval history,” Clemson archaeologist Michael Scafuri said in the release.

Scientists working on the investigation say if the pipe did burst, it could have let in enough water to sink the sub in three minutes, the release explains. Archeologists hope to figure out if the pipe broke during the sub’s mission or if it broke over time as the vessel sat on the seafloor.

The conservation process had led to new discoveries for archeologists studying the Hunley, including more human remains.

Conserving and preserving the H.L. Hunley has been a slow process since the submarine was brought to the surface in 2000. “Removing the concretion was a slow and challenging task for all of us involved, but the ability to get an up-close look at the true surface of the submarine after all this time has made it entirely worth it,” Clemson conservator Johanna Rivera-Diaz said in the release.

“Now that the Hunley has been mostly cleaned of this material, the vessel will sit in a conservation bath for approximately five years to preserve the metal and make her ready for permanent public display,” the press release notes.